Immersion doping method of perovskite films Fabrication of Perovskite Film:SiO2(270 nm-thick) on Si and glasswere used as substrates. The substrates were sequentially sonicated inacetone, 2-propanol, and deionized water for 10 min each. Then, the Si and glass substrates were claned using O2 plasma treatment (200 mT,30 sccm, 50 W) for 120 sec. After dropping 100μL of precursor solution on the prepared substrate, the substrate was rotated at 500 rpm for 5 second then at 4000 rpm for 50 sec with a spin-coater, followed by drying in a nitrogen environment for 5 min and annealing at 100°C for 10 min to fabricate each perovskite filme Figure. 1 (a) Schematic illustration of immersion doping strategy used in this study. Cracks on wafer represents grain boundaries which allows dopant diffusion into the organic spacer layer.(b),(c) Optical microscopy images (left) and cross-sectional (middle) and top surface(right) SEM images of perovskite films (b) before annealing and (c) after annealing at 100 ℃for 10 min. Structural Characterization X-ray Diffraction (XRD): Crystallographic structures of perovskite films were measured by high-resolution X-ray diffraction (HRXRD) technique (Rigaku Smartlab ) Time-of-flight Secondary Ion Mass Spectrometer (TOF-SIMS):Depthpro-file information were obtained using the negative charge ionization po-larity test method as a Cs+, 1 keV, 100 nA etching source in ION-TOF,Germany TOF.SIMS Nuclear Magnetic Resonance (NMR): NMR measurements were per-formed with a 14.1 T Bruker Avance III spectrometer using a 1.3 mm MagicAngle Spinning (MAS) probe equipped at Seoul National University. Samples were packed into 1.3 mm zirconia rotor in an Ar-filled glovebox andwere spun at 62.5 kHz. Rotor-synchronized1Hand207Pb Hahn echo ex-periments were performed with radiofrequency (rf) pulse amplitudes of200 and 175 kHz, respectively. Conditions for1 H-detected207Pb→1H experiments were optimized with207Pb rf amplitudes fixed to 100 kHz. Shifts were referenced to solid adamantane (1H 1.87 ppm) and solid Pb(NO3)2(207Pb –3474 ppm). Figure. 2 (a) Powder XRD of pristine n=1 powder (grey), n=1 powder immersed in DCMsolvent (green for 5 min and blue for 2 hours), and n=1 powder immersed in MB dopantsolution (red). (b) Depth profile of Br− intensity under different immersion duration time (Imm).The inset shows optical microscope images of doped films (c) ) 207 Pb Hahn-echo NMR spectra of pristine and MB-doped BA2 PbI4 (n = 1) samples. Each proton and lead environments are color-labeled

Synthetic routes for IQTPA, IQTPAflu small molecules - 5-Bromoisatin (4.42 mmol) was dissolved in dimethylformamide(DMF) 12 ml, K2CO3 (5.3mmol) and 1-bromobutane (9.0mmol) were added. The solution was stirred at RT for 12h. After extraction with dichloromethane, dried over magnesium sulfate, and filtered. Solvents were removed under reduced pressure and the product was purified by column chromatography. - 5-Bromo-1-butyl-2,3-dione (7.09mmol) was dissolved in acetic acid 40ml and o-phenylenediamine (9.22mmol) was added. The reaction mixture was stirred at 110ºC for 12 hours and extracted with ethyl acetate. Solvents were removed under reduced pressure and the crude residue was purified by column chromatography. - The final indoloquinoxaline-based small molecules, in a Schlenk flask, 9-bromo-6-butyl-6H-indolo[2,3-b]quinoxaline (2.82mmol), (4-(diphenylamino)phenyl)-boronic acid (4.24mmol), and Pd(PPh3)4 (5% mol) were dissolved in toluene. After nitrogen bubbled for 15 min, an aqueous 2M solution of K2CO3 was added to the above solution. The mixture was heated to 90 °C and stirred for 2 days under an N2 atmosphere. Figure. 1 (a) Synthetic routes for InQx-TPA and InQx-Flu (b) UV-vis absorption spectra of IQTPA and IQTPAFlu in film state, (c) Cyclic voltammograms of IQTPA and IQTPAFlu, (d) XPS Pb 4f spectra of perovskite films (e) TRPL decay curves. Characterization 1H and 13C nuclear magnetic resonance (NMR) spectra were measured using a JEOL JNM ECP-400 spectrometer. X-ray diffractometry (XRD) was analyzed by using the Rigaku spectrometer (smart lab) with a Cu Kα source of wavelength 1.5406 Å at a range of 2θ = 10° to 2θ = 80°. UV−visible absorption spectra were carried by JASCO instruments and a Perkin Elmer UV7 Vis Lambda 365 Spectrometer. Ultraviolet photoelectron spectroscopy (UPS) was recorded on the Thermo Scientific Co. measurement. Field emission-scanning electron microscope (FE-SEM) images were measured using Hitachi (S-4800). Steady-state photoluminescence (PL) and a time-resolved photoluminescence (TRPL) were carried out by FlouTime 300 (PicoQuant Co.). Cyclic voltammetry (CV) measurements were analyzed by using VersaSTAT 3 Potentiometry (Princeton Applied Research) with 0.1 M tetrabutylammonium hexafluorophosphate (TBAP, Bu4NPF6) in anhydrous acetonitrile as the electrolyte. The glassy carbon electrodes coated with the IQTPA and IQTPAFlu, and Pt wire as working and counter electrodes, respectively. The silver wire, as the reference electrodes, with a ferrocene /ferrocenium (Fc/Fc+) external standard.

Fabrication of MoS2 field-effect transistors MoS2 and h-BN flakes were mechanically exfoliated from bulk MoS2 and h-BN crystals and transferred to a 270-nm SiO2/p++ Si substrate. After double electron resist layers [methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA)] were spin-coated on the MoS2, the source-drain electrodes were patterned by using an electron beam lithography system. Then Ti (5 nm)/Au (45 nm) layers were deposited by using an electron-beam evaporator. Figure 1. (A) MoS2 prepared by the mechanical exfoliation method. (B) Spin-coated electron resist double layers of MMA and PMMA, followed by hard baking (C) Electron-beam lithography for patterning four-point probe electrodes. (D) Metal electrodes deposited by an electron-beam evaporator. Remote charge transfer doping on MoS2 FETs The dry-transfer method was used to fabricate h-BN/MoS2 vdW heterostructures. The thin h-BN flakes were picked up by adhesive polycarbonate deposited on the dome-shaped polydimethylsiloxane stamp. Then, the h-BN flake was placed on top of the fabricated MoS2 FETs. The heterostructure was dipped into chloroform overnight to remove the remaining polymer residue. The device was annealed at 200°C in an argon atmosphere for 2 hours to improve the interfaces. For the preparation of the BV solutions, the BV dichloride (16.35 mg) was dissolved in deionized water (4 ml) and then toluene (4 ml) was added. Sequentially, sodium borohydride (40 mg) was added and then stirred overnight. When the color of the toluene solution was stabilized in yellow, the upper toluene layer was extracted and then diluted into 1, 2.5, and 5 mM with toluene, respectively. 20 μl of the BV solution was drop-casted and then waited for the solvent to evaporate. Figure 2. (A) The schematic image of BV-doped h-BN/MoS2 FET with Au/Ti contacts for four-point probe measurements. (B) Optical image of h-BN/MoS2 FET before BV doping. (C) AFM image of h-BN/MoS2 FET. (D) Cs-corrected STEM image of the h-BN/MoS2 heterostructure consisting of five layers of h-BN and four layers of MoS2. Characterization Suitable MoS2 and h-BN flakes were located by using an optical microscope, and the thickness of the flakes were measured by an AFM system (NX 10, Park Systems). To confirm SCTD in the MoS2 devices, two-point probe electrical characterizations were performed in a temperature-variable probe station (MSTECH, M6VC) using a semiconductor parameter analyzer (Keithley 4200-SCS). Keithley 4200-SCS with a pre-amplifier was used to measure the voltage drop across the channel by applying constant dc bias for four-point probe measurements.

Device fabrication for characterizing electrical doping Fabrication of Perovskite Film:SiO2(270 nm-thick) on Si and glasswere used as substrates. The substrates were sequentially sonicated inacetone, 2-propanol, and deionized water for 10 min each. Then, the Siand glass substrates were claned using O2 plasma treatment (200 mT,30 sccm, 50 W) for 120 sec. After dropping 100μL of precursor solution on the prepared substrate, the substrate was rotated at 500 rpm for 5 second then at 4000 rpm for 50 sec with a spin-coater, followed by drying in a nitrogen environment for 5 min and annealing at 100°C for 10 min to fabricate each perovskite filme After covering the prepared BA2 PbI4 film with a shadow mask with a channel length of 50 μm and a width of 1 mm, an Au electrode with a thickness of 50 nm was deposited with an electron beam evaporator. Doping with dopant solution was performed by immersing the prepared film in the solution for 2 min. After taking out from the solution, the film was immediately spin-coated at 500 rpm for 5 sec and then at 4000 rpm for 50 sec, followed by drying in a nitrogen environment for 5 min. Figure. 3 Device fabrication steps for electrically doped metal-halide perovskite by using immersion doping method. Electrical Doping Characterization Electrical Measurement: - The I–Vcharacteristics were measured using a semiconductor parameter analyzer (Keithley 4200 SCS). All the measure-ments were performed in a vacuum environment. - Hysteresis, due to ion migration and defects, causes nonlinear I-V curves in halide perovskites, limiting their practical use. To address this, different measurement ranges (0V-10V, -10V-10V, -20V-20V) were tested. The Tukey Test revealed that while average values differed pre and post-doping, conductance across sweep ranges was equivalent. By averaging currents under both forward and reverse biases, a linear I-V curve was achieved, with R-square values of 0.994 to 0.995. This suggests that, despite hysteresis, accurate conductivity values can still be obtained. (a) Current–voltage characteristics (inset; optical microscope images of the films) (b) The measured conductance values presented in box and whisker diagram at each sweep range. The diagram on the right shows the Comparison circles obtained from the Tukey test. The comparison circles have their centers each aligned with the average conductance values and the radii proportional to the standard deviation values of each distribution. The more the comparison circles overlap, the more similar the distributions are.

Dry transfer of hBN & aBN thin film on perovskite/glass substrate The conventional wet transfer method involves immersion in a water, which cause severe damage to perovskite nanocrystals. The new dry transfer method was used to transfer hBN(or aBN) film onto perovskite nanocrystal without immersion in water. It was confirmed that the fluorescence characteristics of perovskite nanocrytsals were well-maintained after dry transfer of the hBN(or aBN) encapsulating layer. Figure. 1 (a) Dry transfer method of hBN(or aBN) thin film on Perovskite/Glass substrate. (b) Scheme of hBN/Perovskite encapsulation and photograph of hBN/Perovskite/Glass. Fluorescence stability test of hBN & aBN encapsulated perovskite It was conformed that perovskite nanocrystals encapsulated with hBN or aBN exhibited less reduction in fluorescence intensity after 6 days of exposure to air compared to those exposed without encapsulation. Figure. 2 Photoluminescence spectra of (a) hBN/CsPbBr3/hBN/Glass, (b) 1 nm aBN/CsPbBr3/aBN/Glass, (c) 6 nm aBN/CsPbBr3/aBN/Glass, (d) CsPbBr3/Glass, (e) CsPbBr3/hBN/Glass, and (f) CsPbBr3/aBN/Glass. Characterization Photoluminescence (PL) spectra were measured by Carey Eclipse fluorometer (Varian, USA).

Synthesis of the quinoxaline-phosphine oxide small molecules (QPSMs) 4-bromo-2,1,3-benzothiadiazole (9.3 mmol) was dissolved in ethanol, then NaBH4 (172 mmol) was added, and the reaction mixture was stirred for overnight at room temperature. After extraction with diethyl ether, the solvent was removed and dissolved again in acetic acid/ethanol solution with the corresponding α-diketone (11 mmol) to further react at 110oC for overnight. The product was purified by column chromatography on a silica gel using DCM/hexane as eluent. The final quinoxaline-phosphine oxide small molecule were synthesized by the Suzuki coupling reaction. The previous synthesized molecules (1 mmol) and diphenyl(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)phosphine oxide (1 mmol) were dissolved in toluene and reacted at 90oC for 48 h under N2 atmosphere with addition of Pd(PPh3)4 (5 mol%) and 2M K2CO3. The synthesized small molecules were purified by column chromatography on a silica gel using EA/hexane as eluent. Figure. 1(a) Chemical structures of QPSMs. (b) Synthetic routes for QPSMs. (c) The optimized geometry, dipole moments, electron density plot from DFT calculation. (d) TGA thermograms, (e) Solid state UV-vis and PL spectra, (f) CV curves, (g) and energy diagrams of QPSMs. Characterization 1H and 13C nuclear magnetic resonance (NMR) spectra were measured using a JEOL JNM ECP-400 spectrometer. UV-visible absorption spectra were recorded on a Lambda 365 spectrophotometer. Photoluminescence (PL) spectra were measure using LS 55 fluorescence spectrometer. Gas Chromatography/Mass Spectrometer (GC/MS) was analyzed by using Agilent 7890GC/5975C MSD. Thermogravimetric Analysis (TGA) was measured using Q500 instrument. X-ray diffractometry (XRD) was carried out using X’Pert3-Powder (PANalytical). Cyclic voltammetry (CV) measurements were carried out by using a Versa STAT3 (AMETEK, Inc.) with tetrabutylammonium hexafluorophosphate (0.1M, Bu4NPF6) as the electrolyte in anhydrous acetonitrile. For CV measurements, a glassy carbon electrode coated with the polymer and a platinum wire were used as the working and counter electrode, respectively. A silver wire was used as a pseudo-reference electrode with a ferrocene (Fc)/ferrocenium(Fc+) external standard.

Growth of hBN and aBN thin films Hexagonal boron nitride (hBN) and amorphous boron nitride (aBN) thin films were deposited through Inductively coupled plasma-chemical vapor depoisition (ICP-CVD). The furnace was heated to the growth temperature (1,200 ~ 1,400 ℃ for hBN and 300 ~ 400 ℃ for aBN) with a carrier gas flow of H2 and Ar. 0.05 ~ 0.2 scccm of Borazine (B3H6N3), serving as the precursor for hBN and aBN, was introduced into ICP-CVD system during the growth time (30 ~ 90 min). The furnace was rapidly cooled to room temperature after hBN (or aBN) growth. The grown hBN(or aBN) thin films were transferred onto SiO2 substrate to measure Raman spectra and AFM images. Figure. 1 (a) UV-vis absorption spectra of tri-layer hBN film on 2-inch sapphiure substrate. (b) Raman spectra of tri-layer hBN, aBN, and SiO2(280 nm)/Si substrate. (c) XPS spectra of aBN thin film for 1s and N 1s. (d-e) AFM image and thickness profile of (d) aBN and (e) tri-layer hBN films. (f) Ellipsometry spectrum of aBN film on Si substrate. Characterization UV-vis absorption spectra were measured by Cary 5000 UV-Vis-NIR spectrometer (Aligent, USA). Raman spectra were measured by alpha300R confocal raman spectrometer (WITec, Germany). X-ray photoelectron spectroscopy (XPS) spectra were measured by ESCALAB 250 Xi X-ray photoelectron spectrometer (Thermo Fisher Scientific, USA). Atomic force microscopy (AFM) images were measured by Dimension Icon (Bruker, USA). Ellipsometry spectrum was measured by M-2000 Ellipsometer (J. A. Woollam, USA).

Synthesis and characterization of mixed-halide 0D perovskites via MCS Precursor salts (CsCl, CsBr, CsI, PbCl2, PbBr2, PbI2, in respect to the desired halide stoichiometric ratio with a fixed total mass of 2.278g) were put in a stainless-steel jar with two-stainless grinding balls (28.65g, 1.9cm diameter) and the jar was shaken with a shaker-type ball mill (Mixer Mill MM-400, Retsch) at 17 Hz for 3 h. The formation of cesium lead halide 0D perovskite(Cs4PbX6) powder samples with mixed-halide compositions through shaker-type MCS was confirmed with various structural and optical analytical techniques. Figure 1. (a) Schematic image of the shaker-type ball mill and photographs of the synthesized powder samples with various halide composition. (b) PXRD patterns, (c) 133Cs ssNMR spectra (at 22kHz MAS and 300K), (d) PL spectra and (e) absorption spectra within the visible range (400-750nm) of the mixed-halide 0D perovskite powder samples. Transferring the powder samples to thin films through flash evaporation 270nm SiO2 on silicon, silicon, and glass substrates were sequentially cleaned with acetone, isopropyl alcohol, and deionized water in a sonicator for 10 min each, then the exposed to O2 plasma using the reactive-ion etching technique (power of 50W, flow of 30cm3/min, and duration of 120 s) to generate hydrophilic surfaces. The synthesized perovskite powder samples were loaded in a tungsten boat, and the cleaned substrates were placed in a vacuum chamber at a height of 30 cm from the boat. The chamber was evacuated to 5 X 10-6 Torr, and the tungsten boat was heated by a current of 140 A. After the deposition, the films were annealed at 150 °C in 1 X 10-4 Torr vacuum for 5 min. PXRD and PL analysis confirmed the transferability of the 0D perovskite structures of the source powder to the deposited films, and FE-SEM images demonstrate the uniform film surface with a thickness of ~250 nm. Figure 2. (a) Schematic image of single-source vacuum deposition. (b) HRXRD pattern, (c) PL spectra of the 0D perovskite films. (d) Top view (left) and cross-section view (right) FE-SEM images of the Cs4PbBr6 film. (e) Images for the 0D perovskite films under UV irradiation without adjusting the color. Characterization X-ray diffraction (XRD) patterns were measured by Rigaku SmartLab diffractometer. Photoluminescence (PL) spectra were measured by JASCO FP-8500 spectrofluorometer. UV-vis absorption spectra were measured by JASCO V-770 UV-vis spectrophotometer. 133Cs solid-state nuclear magnetic resonance (ssNMR) spectra were measured by 600 MHz Bruker ADVANCE III NMR spectrometer with a spinning speed of 22 kHz at 14.1 T. The field-emission scanning electron microscope (FE-SEM) images were obtained by JEOL JSM-7800F.

Temperature-dependent measurements on remote charge transfer doped MoS2 FETs To confirm SCTD in the MoS2 devices, two-point probe electrical characterizations were performed in a temperature-variable probe station (MSTECH, M6VC) using a semiconductor parameter analyzer (Keithley 4200-SCS). Keithley 4200-SCS with a pre-amplifier was used to measure the voltage drop across the channel by applying constant dc bias for four-point probe measurements. The temperature-dependent measurements of the directly and remotely doped FETs were carried out with a cryostat system (CS204*I-FMX-12, Advanced Research Systems). Figure 1. Temperature-dependent mobility values of (A) directly doped, (B) remotely doped devices with a 1-nm h-BN interlayer, and (C) remotely doped devices with a 2-nm h-BN interlayer at temperatures from 10 to 300 K. Identifying suppression of charged impurity scattering in remote doping Theoretical models were introduced for calculating the mobility of directly doped and remotely doped MoS2. The charged impurity-limited mobility (μimp) was calculated as a function of carrier concentration for different impurity concentrations. It was confirmed that the experimentally determined mobility of the remotely doped devices demonstrates a steep increase with the carrier concentration. Figure 2. Experimentally determined mobility (μMoS2) and calculated mobility (μimp) as a function of carrier concentration (nMoS2). The μimp values are calculated for (A) direct doping (green lines) and (B) remote doping (blue lines for the 1-nm h-BN interlayer and red lines for the 2-nm h-BN interlayer) for different impurity concentrations. μMoS2 and nMoS2 values of remotely doped devices with the 1-nm (2 nm) h-BN interlayer are plotted as blue (red) circles and their pristine values are plotted as blue (red) stars, determined at 10 K to minimize the contribution of the phonon scattering. The schematic images of (C) the directly doped device, and (D) the remotely doped device in which the h-BN interlayer suppresses the charged impurity scattering induced by the remote BV2+ dopants.

Synthesis of CsPbBr3 perovskite nanocrystals 1. Cesium oleate is prepared by loading 203.6 mg Cesium carbonate , 10 mL octadecene (ODE) and 0.63 mL of Oleic acid were loaded into a 100 mL three-neck flask. The solution is stirred at 600 rpm and degassed at 120 0 C for 1 hour after which it is heated to 150 0 C under N2 atmosphere. 2. The lead precursor is prepared by mixing 398mg of PbBr2 , 25 mL of ODE, 2.5 mL of OA and 2.5 mL of Oleylamine in a 100mL three-neck flask and degassed at 120 0 C for 1 hour, and heated to 150 0C under N2. 3. The precursor is then heated to 180 for injection. Cesium oleate solution 2 mL is quickly injected with a glass syringe. 4. After 10 s, the flask is cooled down in an ice water bath. The crude solution is purified in MeOAc anti-solvent with a ratio of 1:3 and centrifuged at 8,000 rpm for 3 minutes. 5. Finally the precipitant is then dispersed in hexane and stored in N2 environment. Figure. 1 (a) The synthesis process of CsPbBr3 perovskite nanocrystals using hot injection method. (b) XRD of various of CsPbBr3 samples. (c) TEM image of CsPbBr3 nanocrystals. (d) Different emitting colloidal solutions of perovskite nanocrystals under 365 nm excitation . (e ) Absorbance and PL intensity of synthesized nanocrystals. (f) XPS of the halide element of the nanocrystals for varying CsPbBr3 samples. Characterization The UV-vis absorption spectra were recorded by Varian 5E UV/VIS/NIR spectrophotometer. X-ray diffraction (XRD) was conducted using an X’Pert-MPD diffractometer (Philips, Netherlands). Photoluminescence (PL) spectra were measure using Photon Technology International Flourometer (PTI, USA). Fourier Transform Infra-Red Spectroscopy (FTIR) was measured using JASCO(FT-4100). Transmission electron microscopy (TEM) were performed using a Hitachi H-7500. The films for TEM measurement was prepared by diluting colloidal solutions in hexane solution and dropped mesh grid with a pipette and dried in vacuum . The XPS analysis was performed using KRATOS Analytical system. For measuring XPS, the nanocrystals were spin-coated on glass substrates.

Fabrication of LED devices- 1. ITO-coated glass substrates were cleaned in an ultrasonic bath with deionized water, acetone, and IPA for 15 min and dried in the oven at 80 ◦C overnight. 2. They were then treated with plasma for 15 minutes after which they were transferred to the glovebox. PEDOT:PSS (AI4083) was spin-coated at 4500 rpm for the 40s and dried for 10 min at 140 ◦C in air. Poly-tbd (5mg/ ml in chlorobenzene) was spin-coated onto the PEDOT:PSS layer at 4000rpm for 40s followed by annealing at 120 ◦C for 5 minutes. 3. The perovskite nanocrystals dispersed in octane (5mg/ml) were deposited on the substrate by spin-coating at speed of 2000 rpm for 20 s . 4. Finally, TPBi (60 nm), LiF (1 nm) and Al (100 nm) were sequentially deposited by thermal evaporation under 5 × 10–7 Torr. The full structure of the device was : ITO/PEDOT:PSS/Poly-tbd /perovskite/TPBi/LiF/Al. Figure. 1(a) Schematic diagrams of the deposition of colloidal solution onto the ITO- glass substrate. (b) CsPbBr3 films covered with epoxy. (b) Energy levels of the device structure of the Peled. (c) Photograph of the emitting intensity of the Peled. ( e) Electroluminescence spectra of fabricated Peled devices. Characterization The UV-vis absorption spectra were obtained by Varian 5E UV/VIS/NIR spectrophotometer. X-ray diffraction (XRD) was conducted using an X’Pert-MPD diffractometer (Philips, Netherlands). Photoluminescence (PL) spectra were measure using Photon Technology International Flourometer (PTI, USA). Fourier Transform Infra-Red Spectroscopy (FTIR) was measured using JASCO(FT-4100). Transmission electron microscopy (TEM) were performed using a Hitachi H-7500. The films for TEM measurement was prepared by diluting colloidal solutions in hexane solution and dropped mesh grid with a pipette and dried in vacuum . The XPS analysis was performed using KRATOS Analytical system. For measuring XPS, the nanocrystals were spin-coated on glass substrates. Steady-state PL spectra were measured using a F-7000 fluorescence spectrometer (Hitachi, Japan) by photoexciting the samples at 375 nm. The current J− V− L curves of the PeLEDs were measured using a Keithley 2450 source measure unit combined with a UVIS-50 spot photodetector.

Fabrication of photoelectronic device 1. ITO-coated glass substrates were cleaned in an ultrasonic bath with detergent, deionized water, acetone, and isopropanol for 15 min and dried in the oven at 80 ◦C overnight. 2. After treatment with UV/ozone for 30 min, PEDOT:PSS (AI4083) was spin-coated onto the ITO-coated glass substrate at 4500 rpm for the 40s and dried for 10 min at 140 ◦C in air. Then the PVK was sipin-coated onto the PEDOT:PSS layer at 4000rpm for 40s followed by annealing at 130 ◦C in the glovebox. 3. The perovskite precursor solution was deposited on the substrate by spin-coating at speed of 5000 rpm for 15 s with instant chlorobenzene (CB) solvent cleaning during spinning. ,Then a scotch tape (3 M) was closely pasted on perovskite precursor film, then, the sample was annealing at 100 ◦C for 10 min. 4. Finally, TPBi (60 nm), LiF (1 nm) and Al (100 nm) were sequentially deposited by thermal evaporation under 5 × 10–7 Torr. The full structure of the device was : ITO/PEDOT:PSS/PVK/perovskite/TPBi/LiF/Al. Figure. 1(a) Schematic diagrams for the encapsulation growth method of quasi-2D (PMA)2Csn-1PbnBr3n+1 perovskite films. GIWAXs patterns and corresponding schematic illustrations of quasi-2D (PMA)2Csn-1PbnBr3n+1 perovskite films fabricated by (b) conventional and (c) encapsulation growth method. Characterization The absorbance and XRD spectra of the perovskite films were measured using a Varian 5E UV/vis/NIR spectrophotometer and an X’Pert-MPD (Philips, Netherland), respectively. The film morphologies were obtained by AFM (BRUKER, Icon-PT-PLUS), SEM (S-2700, Hitachi, Japan). Steady-state PL spectra were measured using a F-7000 fluorescence spectrometer (Hitachi, Japan) by photoexciting the samples at 470 nm. Time-resolved PL measurements were recorded using a time-correlated single photon counting equipment (PicoQuant, Germany) with a 470 nm picosecond pulsed laser source (PicoQuant, LDH-P-C-470) and laser drivers (PicoQuant, PDL 800-D. The TEM images were performed on a Hitachi H-7500. The transient photo-conductivity of quasi-2D perovskite films was test according to previous study The confocal PL images were measured using an LSM 780 NLO laser scanning confocal microscope (Carl Zeiss) with a 100× oil immersion objective (a PlanAPO, NA = 1.46) with a 405 nm excitation diode laser. The EL spectra of the PeLEDs were measured using an SR-3AR spectrophotometer. The current J− V− L curves of the PeLEDs were measured using a Keithley 2450 source measure unit combined with a UVIS-50 spot photodetector. An impedance analyzer (1260 Impedance/Gain-Phase Analyzer, Solartron) was used to confirm the existence of the trap state of various samples. The EQE of the perovskite LED were recorded simultaneously by a commercialized system (XPQY-EQE, Guangzhou Xi Pu Optoelectronics Technology Co., Ltd.) that was equipped with an integrated sphere (GPS-4P-SL, Labsphere) and aphotodetector array (S7031–1006, Hamamatsu Photonics).